Striking tools such as hammers, axes, hatchets, picks, adzes and mattocks are subjected to tremendous forces and moments during use. The tools are swung at great speeds and their heads are brought to a halt in fractions of a second and in very short distances. As a result, great kinetic energy is rapidly absorbed by the head and handle and by the object being struck. This energy creates substantial forces on the head, handle and object, and, in particular, on the connection between the head and handle.
Such tools are also subjected to tremendous centripetal forces as their massive heads are rapidly swung by their handles. These forces tend to pull tool heads off of their handles while the tools are in motion.
Further, because the travel of such tool heads is in a generally circular path, they possess significant rotational kinetic energy which is rapidly dissipated upon impact. Such tools are thereby subjected to significant impact-related rotational forces, in addition to the translational forces mentioned above, which cause failure of the head and handle. Additional forces are created when such tools are used for prying, such as to remove nails or dislodge ore.
A typical method of fastening tool heads to handles is to insert a portion of a tool handle through a vertical opening in the head and secure it with a wedge. This technique has been used for many years for wooden handles and has been used in various forms with plastic or composite material handles. An example is disclosed in U.S. Pat. No. 3,770,033 to Gavillet et al. Such tool heads suffer because of reduced cross-sectional area in regions where the hole is located, however. This smaller cross-sectional area causes structural weakness in and potential failure of the tool head. The head of such a tool also may separate from the handle while the tool is being swung after prolonged use or abuse and repeated cycles of impact.
Efforts to overcome the possibility of heads separating from handles of such tools include configuring heads to have a forward striking portion connected to a rear mass or striking portion by a member having smaller cross-section perpendicular to the striking direction. A plastic handle for such a tool may be molded or wrapped around the narrow member during manufacture. While this configuration presents some advantages for attachment of the handle, such heads frequently fail, however, because of the inability of the connecting member with its reduced cross-section area and moment of inertia to absorb the tremendous forces and moments placed on it by the rear portion of the head which must be supported as the head is brought to an abrupt halt from its circular path of travel.